This invention relates to an apparatus and method for regulating the exposure of an active surface. In particular, this method and apparatus are used to detect the presence of pollutants and toxins in the environment.
U.S. Pat. No. 4,115,067 and 4,032,297 both describe a pollutant gas-sensitive substrate in the form of an elongated strip that can be intermittently advanced to provide a series of fresh, light-reflective surfaces sensitive to the pollutant gas. The pollutant gas reacts with the surface causing a decrease in the reflectivity thereof. Measuring a decrease in the light-reflectivity serves to indicate the concentration of the pollutant gas.
U.S. Pat. No. 4,338,094 discloses a process for detecting antigens in a biological sample wherein a particulate supported antibody is loosely encapsulated or confined within a porous filter membrane material. The liquid biological sample can pass through the porous membrane to react with the antibody.
U.S. Pat. No. 4,234,316 relates to a device for delivering measured quantities of a plurality of water soluble reagents to an assay medium. Each reagent is incorporated in a carrier binder. By choosing binders that dissolve or disburse in water at different rates, a rate of reagent delivery as well as the sequence of delivery of different reagents can be controlled. A list of carrier materials is provided.
U.S. Pat. No. 4,434,153 discloses a time release delivery device for beneficial drugs. The materials forming the device wall can be selected to release the drug by different physical-chemical mechanisms such as erosion, diffusion, osmosis, and metabolism. The outer wall of the device can also be provided with various thicknesses as an additional aid for providing timed release of the drug.
U.S. Pat. No. 4,225,575 relates to a device for conducting chemical reactions at a liquid-solid interface. A reaction component is fixed on the surface of a dip stick type device to be immersed in a second liquid reaction component. No protective surface is provided for the fixed reaction component.
Other U.S. patents relating to the release of a reagent are U.S. Pat. Nos. 4,188,447; 4,275,031 and 4,448,548. Additionally, U.S. Pat. No. 4,260,392 relates to a reagent impregnated gel.